1. Field of the Invention
This invention relates to a method of producing a carbon coated membrane and the resulting product and more particularly to a carbon coated ceramic membrane of reduced pore size and modified surface properties having increased chemical, thermal and hydrothermal stability over an uncoated ceramic membrane.
2. Background of the Invention
Ceramic membranes have a variety of uses in industry. They are widely used for separating processes and more particularly microfiltration and ultrafiltration. Ceramic membranes are also potentially useful in high temperature catalytic reaction processes with hydrocarbon streams, such as the dehydrogenation of ethylbenzene to styrene.
One type of ceramic membrane consists of a multi-layer, asymmetric structure with layers of alpha alumina of varying pore size deposited on an alpha alumina support. A final top layer of gamma alumina is deposited on these alpha alumina layers. As is known, the gamma alumina is a transitional alumina and will undergo a phase transformation at elevated temperatures to the more thermodynamically stable alpha form. This transformation is accelerated by the presence of water. This transformation is undesired because the alpha alumina has a lower surface area resulting in a larger pore size. As the transformation takes place, pore size grows and separation efficiency drops.
U.S. Pat. No. 4,865,739 discloses a carbon-coated membrane and process for producing the same. The process consists of depositing at least one layer of a stable emulsion of mineral particles in a solution containing a cokable thermosetting resin. That resin undergoes a polycondensation treatment, followed by coking. The coke formed ensures both the mechanical connection of the mineral particles to one another and to the support.
Butterworth et al., "Carbon-Coated Alumina As A Catalyst Support", Applied Catalysis, 16 pages 375-388 (1985) discloses carbon deposition on a gamma alumina support by liquid-phase carbonization of anthracene or the vapor-phase pyrolysis of propylene. This article is concerned only with alumina powder.
There is still a need for a method of efficiently and effectively producing a carbon coated ceramic membrane having the desired properties of reduced pore size and chemical, thermal and hydrothermal stability.